1. Field of the Invention
This invention relates to a system for supplying a plurality of pallets one after another to the machining center of a machine tool.
2. Description of the Prior Art
There are two ways of storing the pallets which are going to be supplied to the machining center of a machine tool. One of the ways is to stock a plurality of pallets in a horizontal plane and the other way is to stock them in a vertical plane or stack. The former has the disadvantage of requiring a very large floor space if a large number of pallets are stocked. The latter way has the advantage of requiring only a small floor space. Two systems are available for carrying it out. One of them includes a rotatable drum and an elevator installed outside the drum. The vertical movement of the elevator and the rotation of the drum in an indexed pattern are utilized for loading or unloading a particular pallet. The drum is very large and heavy. The pallets and the workpieces carried thereon add to the total weight of the load which must be rotated in an indexed pattern. It is difficult to rotate them quickly in an accurately indexed way. A drum having a larger radius is required for carrying a larger stock of pallets and makes more difficult the problem which has hereinabove been pointed out.
The other system includes a plurality of fixed racks arranged along a plurality of horizontal lines in a vertical plane. It requires a smaller floor space than the system including a drum. It, however, includes a stacker crane adapted for traveling along the racks to load or unload the pallets. This crane is expensive. Moreover, the traveling crane requires a floor space which is substantially equal to the space occupied by the racks. Therefore, the system still requires a considerably large floor space.